1. Field of the Invention
This invention relates to a method and apparatus for detecting underground obstacles, in particular, plastic pipe encountered in the path of guided drilling operations. More particularly, this invention relates to a method and apparatus for detecting underground obstacles by using the sound generated by the guided drill head that is reflected off the obstacle. This sound is then detected by sensors and analyzed.
2. Description of Related Art
Many underground utilities are installed by drilling a hole and pulling the utility through (guided directional drilling). In some cases, it is possible for the drill to penetrate existing utilities, thereby causing, for example, a gas leak that might cause damage, injury or even death. In other cases, gas lines could inadvertently be installed through sewer or other utility pipes. In the process of clearing the sewer pipe, the gas lines could be broken. This would fill the sewer pipe with gas that could be carried to several buildings, leading to explosions that could cause damage, injury, or death.
Using the current state of the art technology, underground objects are detected using acoustics or ultrasound by transmitting a pulse into the ground and sensing the return echo from the underground object. The time of the echo return in conjunction with the propagation velocity of the pulse provides the distance to the object, and the beam shape or triangulation or image reconstruction determines the lateral position of the object. However, such methods are not suitable for use in connection with simultaneous drilling operations as the amount of noise generated by the drilling operation is likely to interfere with the detection process. Accordingly, it is clear that there is need for a technology capable of detecting underground obstacles, in particular, utility pipes in the path of underground drilling simultaneously with the drilling operation.
Accordingly, it is one object of this invention to provide a method for detecting the presence of an underground object in the path of an underground drilling operation.
It is another object of this invention to provide a method for avoiding contact with underground obstacles during drilling operations.
It is yet a further object of this invention to provide a system for detecting the presence of an underground object in the path of an underground drilling operation.
These and other objects of this invention are addressed by a method for detecting an underground obstacle in which a plurality of acoustic signal sensors are deployed in a predetermined pattern on an area of ground defined by a guided drill path having a drill head insertion point. The drill head of a drill is inserted into the ground at the drill head insertion point after which drilling of a borehole in the ground along the guided drill path is commenced. A noise signal generated by the drill head is detected at at least two of the acoustic signal sensors and a difference in arrival time of the noise signal at the at least two acoustic signal sensors is determined. The difference in arrival times of the noise signal is then analyzed, whereby the presence or absence of the underground obstacle is determined. Obstacles that are not normal to the direction of the drilling operation, such as pipes that are oriented in a skew direction, are detected by using two or more rows of acoustic signal sensors and processing the signals to detect and locate off-axis pipes. The obstacles to be detected may be under roads or sidewalks of concrete or other materials. In these instances, the acoustic signal sensors can be placed on the surface of these materials to detect the obstacles.
The system for detecting the presence of an underground object in the path of an underground drilling operation in accordance with this invention comprises at least one noise signal generator adapted for drilling boreholes in the ground along a guided drill path, that is, a drill head of a drill, a plurality of acoustic signal sensors disposed in a predetermined pattern on an area of ground defined by the guided drill path, means for measuring an arrival time of the noise signal generated by said noise signal generator at each of the plurality of acoustic signal sensors, and obstacle means for determining the presence or absence of the underground obstacle in the guided drill path using a difference in the arrival time of the noise signal between at least two of the plurality of acoustic signal sensors. The key to the system of this invention is that no other type of noise signal generator is required to carry out the method of this invention.